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Add a dead code elimination pass #1749
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Activity
as per IRC conversation w/ nmatsakis: The only trick is that many functions are "accidentally" exported due to the "export all by default" rule. One solution is to warn anyway if a function in a module with no export decls is unused (within the crate). Adding explicit export decls suppresses the warning.
We've discussed in the past inverting the "everything exported by default" rule at crate top-level. That is: only export explicit stuff for linking. The intra-crate is intended to make code less chatty and bureaucratic, but linking is often the appropriate time for bureaucracy.
Also note: if you have an explicit export list from a crate, you have a lot fewer roots to run your dead-code analysis from.
Visiting for triage. There have been lots of changes to privacy and similar, but I think this is still true.
I'm thinking of working on this for a class project but I'm unfamiliar with the internal of rustc. tjc has told me to focus on adding warning for now, and then work on eliminating dead code if I still have time, so I have been looking inside librustc/middle to figure out what to do. Since this issue is about adding a new pass and (I presume) the logic is similar to the liveness analysis in librustc/middle/liveness.rs, does that mean I'm supposed to create a new file in librustc/middle/ (say foo.rs) with a top-facing pub fn check_crate that does something similar to liveness.rs, and then call middle::foo::check_crate inside librustc/driver/driver.rs? Also, is there difficulty in checking for unused non-exported functions inside the existing liveness.rs rather than doing a separate pass?
(sorry if the above are stupid questions)
Can be closed?
It can indeed, thanks @ktt3ja!
Add a pass that warns about non-exported functions that are never called.